1. Technical Field
The present invention relates to a method of formation of a black ceramic surface layer or coating upon a substrate of an alloy of titanium.
2. Prior Techniques
The development of a color coating or surface upon titanium and alloys thereof has, in the prior art, been limited to the use of chemical and electrolytic means for the accomplishment of the same.
For example, U.S. Pat. No. 6,093,259 (2000) to Watanabe, et al entitled Color Development of Metallic Titanium, and Black and Colored Titanium Manufactured by this Method, teaches the treatment of developing color upon metallic titanium by treatment of the same with an alkali solution followed by the application of titanium nitrides to produce a finish or surface effect. The use of such titanium nitride powder occurs at temperatures in a range of 800 to 1200 degrees C. Variations thereof taught by Wantanabi include the use of lower temperatures (350 to 600 degrees C.), however for time periods in the range of five to ten hours. The invention of Wantanabi enables the application of a wide range of colors to surfaces of pure or essentially pure titanium, using the a treatment by said alkali solution at a first temperature followed by treatment with nitride powers at a second and higher temperature.
U.S. Pat. No. 5,876,633 (1999) to Coleman, entitled Electrochromic Metal Oxides teaches the use of a range of electro chemical potentials in the presence of mobile ions in combination with a tin oxide doped with electro chemically effective amounts of antimony or niobium in order to provide a range of chromic surface effects as a function of applied electrical potential.
A related teaching exists in U.S. Pat. No. 5,811,794 (1998) to Kurze.
U.S. Pat. No. 5,075,178 (1991) to Schmidt, et al, entitled Black Surface Layer on Light Metal, teaches the development of a black surface layer upon a light metal or alloys of titanium through the use of a particular electrolyte.
U.S. Pat. Nos. 5,820,707 (1998) and 5,868,879 (1999) both to Amick, et al, and both entitled Composite Article, Alloy and Method, teach the use of a mixed oxide ceramic made of selectable combinations of titanium, zirconium, hafnium, molybdenum and tantalum. The teachings of Amick, et al, while relating to oxidation of titanium rich alloys, entail process which operate at temperatures far in excess of that addressed herein and employ time periods for heating or baking which are far less than that contemplated in the present invention. Further, the processed titanium alloy; however, the focus of Amick is that of production of materials having particular application in medical, surgical and industrial applications. Yet further, there is no apparent recognition of the chromatic or ornamental aspects, if any, of the technology thereof. In particular Amick""s only reference to color, as a consequence of his technology, is a reference to a blue-black oxide film which was produced in one of the embodimnents discussed in said U.S. Pat. No. 5,820,707. Further, the timeframe of baking used in the instant invention is materially less than in Amick. Also, no quenching is employed.
The present invention, unlike that above referenced to Wantanabi, does not require use of an alkali or other solution, nor does it include use of an electrolyte as in the case in Schmidt and Coleman referenced above. Accordingly, although Wantanabi and Schmidt make reference to the possibility of providing a black surface layer upon an alloy of titanium, the methodology thereof bears no relationship to that set forth herein.
The technology of Amick, while more closely related to that of the within inventor requires, as above noted, the use of zirconium as a part of its metal alloy substrate and, as,well, operates at both temperatures and within periods of exposure to such temperatures that, are entirely dissimilar to that taught herein.
This invention flows from the recognition that titanium and niobium constitute the most necessary elements of a substrate alloy required in a low temperature, non-electrolytic method to produce articles having an black ornamental finish or surface having broad application in the areas of jewelry, and casings and housings for industrial products, this at a cost well below that of black anodization of steel.
The instant invention relates to a process for forming a metallic article having a black ornamental surface. This process comprises the steps of metallurgically providing an alloy containing between about 51 and 70 about percent by weight of titanium, between about 3.0 and about 17 percent by weight of niobium, and the balance of a metal selected from the group consisting of zirconium, tantalum, molybdenum, hafnium, or chromium, and mixtures thereof. Said alloy is then casted and/or metal worked into a workpiece having a desired geometry and surface texture. The workpiece thereof is then baked in a kiln or oven in a substantially air atmosphere of between about 450 and about 850 degrees C. for a period of between about one and about 29 minutes. Resultant of such baking, there is produced a luminous and durable black surface layer consisting substantially of an oxide of niobium which is adhered to the substrate of the workpiece which remains unoxidized.
It is accordingly an object of the invention to provide a cost-effective process of forming a metallic article having a black ornamental surface.
It is another object to provide a process of providing an article of the above type having sufficient strength, hardness, adherence to its substrate, and reflectivity value in the production of high value molded articles of jewelry and surfaces of casings or housings of industrial products.
It is a yet further object of the invention to provide a process of the above type for the production of such articles having a highly reflective black surface without requirement for use of chemicals, electrolytes, electricity, or complex heat treating apparatus.